1. Field of the Invention
The present invention relates to a plasma processing system and a sample processing method, and particularly to a plasma processing system and sample processing method suited for forming a fine pattern in the semiconductor production process. It relates more particularly to an apparatus or a sample processing method to measure plasma emission in a process chamber and the state of thin film on the surface of such a sample as wafer.
2. Related Background Art
A plasma processing apparatus is extensively used in the fine working phase such as etching, film formation and ashing of the semiconductor production process. In the plasma processing apparatus, the process gas introduced into a vacuum chamber (reactor) is converted into plasma by a plasma generating means, and is made to react on the surface of a semiconductor wafer to provide such treatment as processing of fine holes and grooves or film formation. Furthermore, the required treatment is provided by discharging volatile reaction products
In this plasma processing apparatus, attempts have been made to detect the end point of the etching process by detecting the radiation from plasma during processing, and to measure the film thickness and etching/film forming rate from the reflective light and interference signal on the thin film of wafer surface for plasma radiation in real time, thereby improving the plasma processing accuracy. For example, Official Gazette of Japanese Patent Laid-Open NO. 136098/1993 discloses a parallel plate plasma etching system where two or more plasma receiving sensors are installed on the surface of the electrode opposite to the wafer, and uniform plasma density is ensured by obtaining information on the rate, film thickness uniformity and distribution from plasma radiation strength at multiple points of the wafer.
Official Gazette of Japanese Patent Laid-Open NO. 148118/1991 discloses a parallel plate plasma etching system where laser beam is applied to the wafer from the upper position through a top plate electrode, and the volume of etching is measured through the reflected laser beam, thereby detecting the end point. To avoid contamination of the top electrode according to said Gazette, this system has a hole with a diameter of about 10 mm formed on the portion of the quartz-made electrode cover where laser beam passes, and measures the volume of etching with high accuracy without laser beam being damped even if the electrode cover is contaminated; this ensures stable detection of an end point.
The methods described above, however, have the following problems: For monitoring of the state of thin film or the like on the wafer surface, it is preferred to measure from the upper position opposite to the wafer or from the upper position at an angle of about 45°. The plasma processing apparatus which allows measurement in such a manner is restricted in the measurement method and structure. In the microwave ECR method and inductively coupled plasma processing apparatus, for example, a quartz-made transparent window and plate may be installed above the wafer in order to apply microwaves inside the process chamber or to introduce inductive electric field. In this case, the state of the wafer surface can be measured from above. However, in the so-called capacitatively coupled parallel plate plasma processing apparatus, the top electrode opposite to the wafer is made of conductive metal such as aluminum, so it is not structured to allow the surface of the wafer to be directly penetrated. For this reason, measurement of the wafer surface requires a sensor for a plasma radiation to be installed on the surface of the electrode opposite to the wafer, as indicated in the Official Gazette of Japanese Patent Laid-Open NO. 136098/1993. However, reaction products are deposited on the sensor for a plasma radiation according to repeated electric discharges. This makes it very difficult to ensure stable measurement for a long time.
One of the attempts to solve this problem is the method disclosed in the Official Gazette of Japanese Patent Laid-Open NO. 148118/1991. A hole having a diameter of about 10 mm is formed on the measurement portion of the quartz-made electrode cover directly exposed to plasma where laser beam passes, thereby eliminating an adverse effect on measurement, despite the deposit membrane formed on the quartz-made cover surface. However, this method does not ensure stable measurement. To get the specified plasma density required for plasma processing, high-frequency power amounting to several kilowatts of high power is applied to the top electrode. If an about 10 mm-diameter hole is formed on the electrode and electrode cover as disclosed in said Official Gazette, local abnormal discharge will occur to the hole, or plasma will enter the hole, and the top electrode and electrode cover may be damaged. Furthermore, bias is applied to the top electrode, the top electrode will be sputtered by ions in plasma through the hole on the electrode cover. Since the top electrode is made of such a metal as aluminum, it may be damaged or entry of particle contamination may result.
Needless to say, the wafer surface can be measured in principle from the side wall of the process chamber at a smaller inclination, instead of from the upper position opposite to the wafer. However, an opposite plate type where such a plate as silicon is placed opposite to the sample at a position several tens of millimeters away is often adopted especially in the oxide film etching system, in order to control excessive dissociation of process gas and to improve process reproducibility. In this case, the angle of measuring the wafer has to be about 10° in practice. It is also difficult to ensure satisfactory measuring accuracy. Under these circumstances, it has been hoped that the state of wafer surface can be measured from the top opposite to the wafer in the opposite plate type plasma processing apparatus as well.
With reference to the microwave ECR system and inductively coupled plasma processing apparatus, authors of the present invention have described that wafer surface can be measured from a quartz-made transparent window above the wafer. However, reaction products are deposited on the quartz-made window surface as discharge is repeated, and transmittance is reduced. Conversely, surface is etched and is made rough, so stable measurement for a long time is difficult. For this reason, this system has failed to meet practical requirements.